The invention relates to power conversion apparatus and methods and, more particularly, to inverter apparatus and methods of operation thereof.
Inverters are used in a variety of different power systems applications, including uninterruptible power supplies (UPSs), power conditioners and generator/utility grid interfaces. In a typical on-line UPS, for example, a rectifier may be used to provide power to a DC bus from an AC source, such as a utility source, and a battery may be coupled to the DC bus to provide auxiliary power to the DC bus when the AC source fails. An output inverter coupled to the DC bus may be used to generate AC powers. Other types of UPSs may not utilize an input rectifier, but may include similar output inverter coupled to a DC bus that is powered by a backup battery along similar lines.
A variety of techniques have been developed to improve the performance of inverter apparatus. For example, U.S. Pat. No. 7,088,601 to Tracy et al. describes a power converter apparatus, such as an on-line or line-interactive UPS, that includes a DC/AC converter that is coupled to first and second DC busses. A voltage range between the DC busses is shifted with respect to an output neutral using, for example, a half-bridge circuit that is configured to selectively couple the DC busses to the neutral. Such a neutral coupling technique may be used to reduce switching losses and component stress. U.S. Pat. No. 7,046,527 to West describes an inverter for use in connecting distributed energy systems (e.g., photovoltaic arrays, fuel cells, wind turbines and the like) to a utility grid, the inverter including multiple, high frequency switching elements that are operated in a synchronous, time-skewed arrangement to provide potential reduction in ripple current.